1. Field of the Invention
The present invention relates to an ink jet recording head adapted to perform recording on a recording medium by discharging ink from a discharge port, and to an ink jet recording apparatus including the ink jet recording head.
2. Description of the Related Art
An ink jet recording apparatus performs recording by discharging ink droplets from a discharge port provided in an ink jet recording head, and applying the ink droplets to a recording medium such as paper or resin sheet. A conventional ink jet recording head includes a substrate bearing an energy generating element, a flow path member bonded to the substrate for forming ink flow paths, and an orifice plate bonded to the flow path member and having an ink discharge port. The energy generating element is provided in a position corresponding to the ink flow path, which is used to generate energy to discharge ink. Examples of the energy generating element include an electrothermal converting element such as a heating resistance element, a piezoelectric element, and so forth.
Ink mist accompanying the discharged ink droplets is also generated by the inkjet recording head when ink is repeatedly discharged. Ink mist may cause the problem of displacing an ink discharge direction when the ink mist adheres to the discharge port face of the inkjet recording head. FIGS. 8A to 8D illustrate this problem.
FIG. 8A shows a state of ink mist 110a adhering on the discharge port face surface (100a) near a discharge port 101 on an orifice plate 100. When ink 110 is discharged in this state, the ink 110 is drawn towards and combined with the ink mist 110a that adheres to the discharge port face 100a, after passing through the discharge port 101, as shown in FIG. 8B. As a result, a displacement in the ink discharge direction of the ink 110 occurs at the discharge port 101 as shown in FIGS. 8C and 8D. When the ink discharge direction is displaced, an impact position of the ink 110 onto a recording medium is displaced, thus degrading the image quality. The displacement of the ink discharge direction is also referred to as a “drag”.
In order to prevent the displacement of the ink discharge direction caused by ink adhering to the discharge port face, a conventional ink jet recording apparatus is configured to perform a wiping process for wiping off the ink adhering to the discharge port face of the ink jet recording head using a blade made of rubber. However, the ink that adheres to the discharge port face cannot be completely wiped off even after the wiping process, so that the some ink still remains on the discharge port face in some cases.
Japanese Patent Application Laid-Open No. 2000-326515 discusses applying a water-repellent (ink-repellent) treatment to the discharge port face in order to effectively wipe off the ink adhering to the discharge port face. Moreover, Japanese Patent Application Laid-Open No. 2001-71510 discusses an ink jet recording head having an orifice plate in which a protective film having an ink-repellent property is formed at an inner side of the discharge port, a top end portion of the protective film is made to protrude from the discharge port face, and an ink-repellent film is formed throughout the discharge port face. The protective film protruding from the discharge port face is configured, during the process for forming the orifice plate, by forming a protective film having an ink-repellent property on the inner wall of the discharge port, and then performing etching to remove a surface of the orifice plate while leaving the protective film.
In general, ink for use with an ink jet recording head includes dye ink (dye-based ink) and pigment ink (pigment-based ink). The dye ink is used to print a high-resolution image such as photographs. The pigment ink is used to print characters or the like. The pigment ink has a characteristic that it can firmly adhere to a material surface compared to the dye ink. Accordingly, a contact angle of an ink-repellent layer of the ink jet recording head using the pigment ink is made larger than that using the dye ink, so that ink can be prevented from adhering to the orifice plate surface.
On the other hand, in recent years, the pigment ink is often used to achieve high-resolution printed matter and improve its preservation. In this case, compared with the case of printing characters, the amount of discharge of ink drops is very small such as about several pl (pico liter), and the nozzle array density is about 1200 dpi. Here, when a conventional ink-repellent layer is provided on the orifice plate, it is newly found that the contact angle decreases in part in some places adjacent the discharge port, that is, a deterioration of the ink-repellent layer occurs near the discharge port, regardless of the presence of ink firmly adhering to the orifice plate.
This phenomenon is not observed in ink jet recording heads using dye ink. The problem has recently been detected in a recording head having a high density array for discharging minute droplets using pigment ink to record a high-resolution image as described above.